1. Field of the Invention
This invention refers to railway switching machines, and, in
particular, to those devices which are used to move the rail end points of switch point assemblies or the movable V-points of movable point frog assemblies.
2. Background Art
As shown in FIG. 1, railway switch point assemblies include two rail end points which are tapered rail profiles capable of deflecting to move between two different positions, in order to facilitate the correct alignment of the track components for the desired path of rolling stock transiting through the switch point assembly. The switch point assembly has two deflectable or movable rail end points A which move in concert with one another between first and second alternative positions. The rail end points A are often interconnected, such as by means of an interconnecting link IL. In a first alternative position, a first one of these movable rail end points A can be aligned with a first fixed stock rail C to facilitate passage of the rolling stock straight through the switch point onto a first set of fixed rails. In a second alternative position, the second movable rail end point A can be aligned with a second fixed stock rail C to facilitate passage of the rolling stock onto a second set of fixed rails, such as to divert the rolling stock onto a siding. In FIG. 1, for example, the right end point A is in contact with the right stock rail C. The remote ends of the two deflectable rails almost intersect, near the location where the second set of fixed rails diverges from the first set of fixed rails. Typically, a motor unit MU drives a switch machine SM, which shifts two connecting rods CR to the right or left, in unison, to move the rail end points A. The motor unit and the switch machine may be installed in a housing H which is adapted to replace a railroad tie, referred to as an “in-tie” installation.
At the ends of the deflectable rails where they almost intersect, it is necessary to provide a means for the rims of the wheels of the rolling stock to cross the fixed rail C which is not being followed, and to pass from one of the deflectable rails onto the desired set of fixed rails. Frog assemblies are used for this purpose, wherein the left rail of one set of rails beyond the frog assembly, and the right rail of the other set of rails beyond the frog assembly form a “V-point” adjacent to the point where the deflectable rails cross. At this point, the remote ends of the deflectable switch point rails can form “wing rails” on either side of the V-point.
Some of these frog assemblies can have a fixed V-point, a fixed wing rail, and a deflectable wing rail which can deflect as the wheel rims pass through, allowing the rolling stock to follow the desired set of fixed rails. These are “fixed point” frog assemblies. Still other frog assemblies can have fixed wing rails and a moving or deflectable V-point which can be aligned with either of the wing rails, according to the desired path of the rolling stock. These are commonly called “movable point” frog assemblies.
The state of the art includes numerous switch point machines for railway split point movements. For example, EP 1,245,469 to Biagiotti describes such a switch point machine. Such mechanisms are normally installed at the switch point, and they are typically applied only to move the split rail end points of the switch point assembly. For operational reliability and safety, it is common to sense the positions of the rail end points, typically with proximity sensors.
Known in-tie switch machines cannot be installed under a movable point frog assembly and used to move the movable V-point. Rather, switch machines for the movable point frog application are installed to the side of the track, some distance from the V-point. As a result, proximity sensors must be placed near linkage elements which are far removed from the V-point itself, resulting in less accuracy and less reliability. One difficulty in adapting any known in-tie switch machines for use in moving the V-point of a movable point frog assembly is that the switch points and the movable V-points are designed for different stroke lengths. That is, switch points are designed for a stroke length of 4.75 inches, while the V-point of a movable point frog assembly is designed for a stroke length of only 3.0 inches.
Therefore, it is desirable to provide a simple type of in-tie mechanism which can be used to adapt a typical switch machine to move the deflectable V-point of a movable point frog assembly. Use of the same type of switch machine in an in-tie installation, to shift either the switch points or the V-point, will simplify the maintenance and operation of the apparatus at a given turnout. Further, provision of an in-tie switch machine for movable point frog applications will enable the placement of proximity sensors near the V-point, but still within the in-tie housing of the apparatus.